Machines such as, for example, off-highway trucks and other heavy construction and mining machines, are used to perform many tasks. To effectively perform these tasks, the machines require a power source that provides significant power to a transmission. The power source may be an engine such as, for example, a turbine engine, diesel engine, gasoline engine, or natural gas engine operated to generate a power output. The transmission may provide a range of gearing in order to allow the machine to work at several different speeds while keeping the engine within a desired operating range. Typically, the machines include a multi-speed transmission that generally includes a series of gears and is connected to the engine via a torque converter. The torque converter may assist with initial start-up and further may provide a broader torque transmission range.
As described in U.S. Pat. No. 5,924,951 to Winzeler et al., a multi-speed transmission for a machine typically includes a variety of gears and clutches that are disposed between an input member and an output member of a machine. The input member is connected to, and is rotated by, an engine via a torque converter. The output member is used to move the machine. The clutches are used to engage different combinations of gears that will connect the input member to the output member through a selected gear ratio. The selected gear ratio translates the rotational speed of the input member, as provided by the engine, to a desired rotational speed of the output member.
To generate the wide range of gear ratios for the machine, the multi-speed transmission typically includes a plurality of intermeshing gears and a corresponding plurality of control elements such as clutches and brakes. Each of the gears may have different numbers of teeth to achieve the desired gear ratios. In addition, differently designed clutches may be used to engage the different gears.
The manner in which the gears are engaged to provide the different gear ratios and the number of different gear ratios impacts the efficiency of the transmission and machine. The larger the step and the more variable the step between gear ratios, the more an engine will deviate from the desired operating range. Energy and efficiency are lost when the machine operates outside of the desired operating range.
More recently, some multi-speed transmissions have been proposed which provide a greater number of forward gear ratios. U.S. Pat. No. 7,575,533 to Gumpoltsberger, for example, discloses a multi-speed transmission having four planetary gear sets, three clutches, and three brakes. The transmission provides nine forward gear ratios and one reverse gear ratio. It may be advantageous is certain applications, however, to provide more than one reverse gear ratio.
Other transmissions have been proposed that provide a greater number of forward gear ratios as well as multiple reverse gear ratios. These devices, however, require an excessive number of gears and/or control elements (such as clutches and brakes). U.S. Patent Application Publication No. 2009/0036252 to Phillips et al., for example, discloses multi-speed transmissions having nine forward gear ratios and up to five reverse gear ratios. Each of the embodiments disclosed in Phillips has 4 planetary gears (including one double pinion planetary gear) and nine control elements in the form of clutches and/or brakes. The excessive number of clutches and brakes make the transmission overly costly to manufacture and assemble. Additionally, these numerous components may generate unnecessary drag between rotating and non-rotating components, which adversely affects fuel efficiency.
The exemplary embodiments disclosed herein of a multi-speed transmission overcome one or more of the performance, fuel economy, and cost issues set forth above. While the embodiments are described in the context of a truck, one skilled in the art will appreciate that this disclosure is clearly applicable to other types of vehicles and machines that require operation in multiple forward and reverse speeds.